The link between abnormalities of brain structure/function and cognitive test performance in ADHD persons is well-established, if poorly understood. There is evidence for smaller right frontal lobe volume, abnormalities in basal ganglia size, and reductions in white matter tracts in persons with ADHD (Castellanos et al., 1994; Castellanos et al., 1996; Filipek et al., 1997; Hynd et al.,1993; Mataro et al., 1997). Prefrontal cortex and basal ganglia are involved in planning, initiation, execution, and supervision of ongoing cognitive and motor functions (Fuster, 1997). Structural brain abnormalities correlate with deficits in these cognitive functions and with impulsive behaviors that are symptoms of ADHD (Casey et al., 1997; Mataro et al., 1997; Semrud-Clikeman et al., 2000). Functional imaging techniques, which quantify neural systems operation with respect to cognitive processes, are particularly valuable tools used to characterize dysfunctional neural networks. The most frequently employed method is electrophysiology, in which small voltage changes on the scalp occurring during task performance are recorded and averaged into waveforms that depict brain function to events of interest. These average EEG waveforms are called event-related potentials (ERPs). ERPs to Go/No-Go tasks are well characterized in healthy, non-clinical samples (Logan, 1994). The most frequently observed component to No-Go trials is a large negative potential occurring approximately 275 msec following stimulus presentation (N2) that has a fronto-central distribution. The large N2 has been interpreted as a reflection of early response inhibition processes. Electrophysiological studies find that the large N2 often seen with successful inhibition is diminished in ADHD children and adolescents (Overtoom et al., 2002; Pilszka et al., 2000; Yong-Liang et al., 2000). A literature review reveals no comparable studies of ADHD adults, so the degree of N2 abnormality in older ADHD persons is not known.